Outdoor panels from Norway spruce: the effect of coating colour on the temperature

Wood used outdoors is often surface treated with a paint to protect the wood from moisture anddeterioration. If coated with a dark colour, the albedo value is lowered. A lower surface albedo generates greater amountsof energy absorption and makes the surface, and subsequently the wood, warmer and dryer. This study was carried out to increase knowledge of how different coating colours impact the temperature of the underlaying wood, and the effect this has on the moisture content (MC). The study was performed by exposing panels of Norway spruce [ Picea abies (L.) H.Karst.] painted with three different colours (white, red, and black) to natural sunlight over a month during summer. Each panel fitted with a dry-bulb humidity sensor inside. The results showed a greater variation in calculated equilibrium moisture content (EMC) in the darker panels, since the temperature reached higher levels than the white panels when exposed to sunlight. The maximum recorded temperature was around 50 °C for the dark panels while the maximum forwhite was around 40 °C. Furthermore, it was shown that the temperature inside the panel reaches its maximum around the same time as the outside air, while the maximum values for EMC were recorded approximately 8-9 hours apart between the panels and the outside air.